Hi Possums - I don't know the answer but my guess is that it shouldn't matter - it is designed to stay in your system for AT LEAST 12 hours and I assume there's definitely a margin of error built in. I had trouble remembering all my shots/sniffs/pills as well. I programed recurring alarms into every electronic device I have (phone, work PDA, work calendar etc.) and that really helped - alarms going off all the time which I'm sure drove peopel crazy, but I didn't forget! I do know that the timing of the trigger shot is very sensitive - so this is the one that I'd make sure to do right on time.